The invention relates to a master cylinder which represents a component of a brake system for automobiles.
A master cylinder is well known in the art which comprises a primary piston disposed to be movable within an axial bore of a housing toward a rear end thereof, a secondary piston disposed to be movable within the axial bore of the housing toward a front end thereof, a first liquid pressure chamber in which a braking liquid pressure is generated as the primary piston is driven forward, and a second liquid pressure chamber in which a braking liquid pressure is generated as the secondary piston is driven forward.
Conventional master cylinders are categorized into xe2x80x9ca port typexe2x80x9d, xe2x80x9ca center valve typexe2x80x9d and xe2x80x9ca plunger typexe2x80x9d.
The master cylinders of xe2x80x9ccenter valve typexe2x80x9d and xe2x80x9cplunger typexe2x80x9d are increasingly finding their applications recently as ABS (anti-skid brake system) is becoming popular.
A conventional master cylinder of xe2x80x9cplunger typexe2x80x9d includes a primary and a secondary piston, between which a piston return spring is held compressed. At this end, the opposite ends of the return spring are provided with retainers, which are fastened to stems, resulting in an increased number of parts, and hence, an increased cost of the master cylinder.
A master cylinder of plunger type also includes a sleeve disposed within the housing and which is formed with an axial groove, which receives a retraction limit member which is integrally formed with a return spring retainer associated with the primary piston. This presents a difficulty in assembly, and also results in a complicated construction and an increased cost.
It is an object of the invention to provide a master cylinder which is relatively simple in construction and inexpensive to manufacture.
Specifically, the present invention relates to a master cylinder comprising a primary piston disposed to be reciprocable within an axial bore of a housing toward a rear end thereof, the primary piston having a step defined between a reduced diameter and an increased diameter portion; a secondary piston disposed to be reciprocable within the axial bore toward a front end thereof and having an axial bore which is open rearward; a first sleeve disposed rearward of the secondary piston and slidably fitted into the inner peripheral surface of the housing; a first reservoir chamber defined by the inner peripheral surface of the axial bore in the secondary piston and the reduced diameter portion of the primary piston and into which a braking liquid from a reservoir is normally introduced; a first liquid pressure chamber defined between the increased diameter portion of the primary piston, the first sleeve and the inner peripheral surface of the housing; and a second liquid pressure chamber defined within the housing at a location adjacent to the secondary piston for generating a liquid pressure as the secondary piston is driven forward. In accordance with the present invention, the reduced diameter portion of the primary piston is slidably fitted into the axial bore formed in the secondary piston, and either the first sleeve or the secondary piston is provided with a retraction limit member which restricts a retraction limit of the primary piston.
With the arrangement of the present invention, no retainers or stems are used which are used in a conventional arrangement for holding the return spring compressed, thus allowing the number of parts used to be reduced a in a conventional master cylinder. Accordingly, it is possible to provide a master cylinder which is simple in construction and inexpensive manufacture in comparison to the prior art.
Above and other objects, features and advantaged of the invention will become apparent from the following description of several embodiments thereof with reference to the attached drawings.